The present invention relates generally to a spark ignition timing control system for a spark ignition internal combustion engine for controlling spark advance corresponding to the engine operating condition. More specifically, the invention relates to a spark ignition timing control system for controlling spark advance in response to an engine knock sensor signal and transmission gear shifting.
Spark ignition internal combustion engines in automotive vehicle use a basic spark timing setting which is advanced with manifold vacuum and engine speed in accordance with a predetermined spark timing schedule. The basic setting, the speed advance, and the amount of vacuum advance, are selected to provide spark timing sufficiently retarded from the timing that creates objectionable engine knock. In establishing the basic setting and the advance characteristics, account is taken of the variations of knocking quality of the fuels likely to be used, the various engine operating conditions likely to be encountered, likely engine deterioration, and other factors that may require greater ignition retard to avoid engine knock. It has not been possible for the conventional spark advance controls to provide the more efficient and responsive engine operation and other advantages that could be obtained if engine knock at undesirable levels was precluded.
With regard to the more effective spark advance controls capable of application to spark ignition internal combustion engines to preclude operation at undesirable levels of engine knock, one approach had been made, which was described in U.S. Pat. No. 4,002,155 to John L. Harned et al, issued on Jan. 11, 1977. Harned et al shows an engine and engine spark timing control with a knock limiting circuit which includes a knock detector for sensing engine knock and a digital programmed spark timing controller. The knock detector produces a detector signal. The number of individual ringing vibrations exceeding a reference signal during a predetermined amount of engine crankshaft rotation is counted. When the number of such counts exceeds a predetermined crankshaft rotation, engine spark timing is retarded. If the number of such counts is less than a predetermined number during the predetermined crankshaft rotation, engine spark is advanced.
In such control systems, feedback control lags due to a lag of response in the system. Although such lag of response may be ignored in the normal and stable driving condition, this lag will possibly cause engine knocking upon shifting-up the transmission gear, particularly in the relatively high or full load condition. Namely, when an automatic transmission shifts up from second gear to top gear or from top gear to over-drive gear, the engine speed is abruptly dropped to the areas possibly causing engine knocking. Therefore, a spark timing control is required which can follow abrupt acceleration or deceleration of the engine and can retard spark timing in response to upshifting of the automatic transmission gear.